The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Hybrid powertrains for motor vehicles employ two or more distinct power sources to propel the motor vehicle. In a hydraulic hybrid vehicle (HHV) a regular internal combustion engine and a hydraulic motor are used to power the motor vehicle. Hydraulic hybrid systems typically include two components: high pressure hydraulic fluid vessels or accumulators and hydraulic drive pump/motors. The accumulators are used to store pressurized fluid. Acting as a motor, the hydraulic drive uses the pressurized fluid to rotate the wheels of the motor vehicle. Acting as a pump, the hydraulic drive is used to re-pressurize hydraulic fluid by using the momentum of the vehicle. This process converts kinetic energy into reusable potential energy and is called regenerative braking. There are two types of HHVs: parallel and series. In parallel HHVs both the engine and the hydraulic drive system mechanically interact with the wheels. The hydraulic pump/motor is often integrated into the differential or final drive unit.
While these systems are effective, there is room in the art for a hydraulic hybrid system having reduced complexity and energy costs while still providing adequate engine stop-start performance and vehicle launch performance that can be packaged in on road vehicles including passenger cars, SUV's, and pick-up trucks.